The present invention relates to a brake control device in an air over hydraulic brake system mounted on an automobile.
In the brake control device of this type, as an air modulator for controlling oil pressure supplied to a wheel cylinder by air pressure, there has been known a structure having an air over hydraulic cylinder containing an air piston on one side and a hydraulic piston on the other side.
The above modulator has a housing integrally formed with a solid valve unit composed of two kinds of solenoid valves (hold valve and decay valve) for controlling the suction, holding and discharge of air to an air chamber side of the air piston.
Further, there may be considered such a brake control device including a traction control mechanism in addition to the above brake control device, as shown in FIG. 4.
FIG. 5 shows the whole construction of a vehicle brake system including this brake control device.
In this figure, a first conduit 46a extending from an air tank 41 as a first pressure source is connected to a brake valve 42. A first conduit 46b extending from the brake valve 42 is connected to modulators 9 provided on the rear side, that is, the drive wheel side. A second conduit 47 extending from an air tank as a second pressure source is connected to a traction control valve 51. A third conduit 48 extending from the traction control valve 51 is connected to the modulator 9. Also, the brake valve 42 is connected to modulators 19 on the front wheel side through a fourth conduit 49.
A speed sensor 39 is disposed on each of the front and rear wheels for detecting rotation of each wheel for feeding the detection signal to a Electric Control Unit 40 (ECU).
In the ECU 40, the traction control valve 51, and the modulators 9 and 19 are activated according to the detection signal from the speed sensor 39 and a brake pedal for controlling the brake of each wheel.
The modulator 9 as shown in FIG. 4 will be explained. A hold valve 4 and a decay valve 5 are disposed in parallel to each other in the modulator 9.
The hold valve 4 has a hold plunger 11 axially movable in a hollow portion of a solenoid coil 13, and a rubber made hold valve main body 26 is provided in the right end (in this figure) of the hold plunger 11. The hold valve 4 is biased in the left in a housing 10 of the modulator 9 by a hold spring 15, and is usually opened to a communicating passage 32 as an air supply passage.
A communicating passage 38 is formed at the right end portion of the valve unit 6. The communicating passage 38 is communicated to three ways, that is, a supply passage 34 for supplying air from the brake valve 42, a supply passage 33 for supplying air from a traction control valve 51 described later and the communicating passage 32.
A shuttle valve device 90 for controlling air flow is provided in the above communicating passage 38.
In the shuttle valve device 90, a shuttle valve piston 91 is slidably disposed in the communicating passage 38, and valve rubbers 92 and 93 are respectively attached on both ends of the shuttle valve piston 91.
In the communicating passage 32, a return valve 28 permitting air flow from a chamber passage 31 to the communicating passage 38 side is biased in the left (in this figure) by a return spring 30.
The communicating passage 32 is connected through the return valve 28 to a hold valve chamber 7, a decay valve chamber 8 and the chamber passage 31.
The decay valve 5 has a decay plunger 12 axially movable in a hollow portion of the solenoid coil 14, and a rubber made decay valve main body 27 is provided at the right end (in this figure) of the decay plunger 12.
The decay valve 5 is usually biased on an exhaust passage 35 side by a return spring 16 to close the exhaust passage 35 communicated to an exhaust valve 36.
The traction control valve 51 as shown in the lower side in FIG. 4 will be described below.
The traction control valve 51 has a pair of valve pistons 53 in the upper side (in this figure) and a pair of solenoid valve bodies 59 in the lower side (in this figure) centered on an air supply passage 57 communicated to a second conduit 47a from an air tank 43. The valve piston 53 functions as a control valve usually closed to the air supply passage 57 by a return spring 56 for controlling the supply of air to an air pressure passage 66b.
In the air pressure passage 66b, one end is communicated to a third conduit 48 and the other end is communicated to an air pressure passage 66a. Also, in the air pressure passage 66a, one end is communicated to the decay valve 62 side of the solenoid valve body 59 and the other end is communicated to an exhaust valve 67.
Thus, air made to flow in the communicating passage 38 from the brake valve 42 and the air tank 43 through the traction control valve 51 is supplied to an air chamber through the hold valve 4 side by activation of the shuttle valve device 90, and also each solenoid valve is activated, to thereby execute the brake control.
However, the brake control device as shown in FIGS. 4 and 5 has a disadvantage of making the construction thereof complex: namely, achieving the traction braking requires the shuttle valve device 90 for controlling air pressure, the exhaust valve 67 of the traction control valve 51 and the accompanying conduits; and further the number of the parts of each device is increased.
Further, by the presence of the conduit between the modulator 9 and the traction control valve 51, the preferable brake responsiveness requires a large flow rate, which enlarges the size of the device.
Taking the above into consideration, the present invention has been made, and the object is to provide a compact brake control device capable of reducing the number of parts and improving the brake responsiveness with a low cost.